To cancel reain delay, you can go to your schedule tab. The date with gray dot beneath is the date with restriction/weather skip. You can select the date, and tap on the sepeicific restirction, it will pop up option for you to cancel.
Please note that rain delay is just one-time setting. It's mainly used when it's raining but the weather forecast data is incorrect, so you can tell Netro that I don't want watering in the next n days. If the weather data is correct, Netro will not water while raining. You should set in settings->preferences -> rain -> days to skip, if you want to set it for all rainy days.